The 3 measuring "legs" spaced 120° apart retract when the pistol trigger is pulled. This creates a self-aligning and self-centering bore gage with 3-line contact. The measuring head can then quickly be inserted into the bore. Releasing the trigger expands the 3 legs and the measurement is given on the attached indicator. The legs are case hardened (carbide) except for the smallest model which has hardened steel legs. The balance of the measuring head is aluminum coated. The Etalon pistol grip bore gage, made by Roch (Europe) and known as Alesotest is designed for measuring not only blind bores, but also through bores. Except for the smallest model covering the ranges .236 to .394 inches (6 to 10 mm) they can also measure short centering shoulders. Each gage consists of an interchangeable measuring head, a pistol grip, setting rings and extensions as outlined in the ordering chart below. The gages are serialized for ISO purposes and the manufacturer provides a certificate of conformity. They are guaranteed to meet factory standards. Certificates of calibration to NIST standards are not provided. These bore gages are sturdy gages, easy to use and ideally suited for part series inspection on the production floor. They come in a wooden case with ample room for gage components. The Etalon pistol grip bore gage (Alesotest) is used in conjunction with a digital dial indicator (included in the complete set) or an optional electronic axial probe. They fit into a 3/8" collet which means that your indicator or probe must have a 3/8" stem diameter. This also means you could use a mechanical dial indicator instead. The measuring head accuracy is 4 µm (.00016 inch) up to 1.968 inches, subsequently 5 µm (.0002 inch). This accuracy is independent of the dial indicator's accuracy. But, most important, repair service and warranty repairs are available through Long Island Indicator Service, ensuring many years of useful life for this important tool. 
Etalon pistol grip bore gage shown with digimatic indicator. You could replace the indicator with a probe or a dial indicator with a 3/8" diameter stem. 
Complete set is shown with 4 measuring heads, one depth extension, two setting rings, wrench and pistol grip in a customized wooden box. Note that there is room for other components including your own dial indicator. The set prices shown below include a digital indicator.
Dimensions are shown in mm. There is no significant dimension "A" for the larger models.
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